Query answering in Ontology Based Data Access (OBDA) exploits
the knowledge of an ontology's TBox to deal with incompleteness of
the ABox (or data source). Current query-answering techniques with
DL-Lite require exponential size query reformulations, or expensive
data pre-processing, and hence may not be suitable for data
intensive scenarios. Also these techniques present severe
redundancy issues when dealing with ABoxes that are already
(partially) complete. It has been shown that addressing redundancy
is not only required for tractable implementations of decision
procedures, but may also allow for sizable improvements in
execution times. Considering the previous observations, in this
paper we present two complementary sets of results that aim at
improving query answering performance in OBDA systems. First, we
show that we can characterize completeness of an ABox by means of
dependencies, and that we can use these to optimize DL-Lite TBoxes.
Second, we show that in OBDA systems we can create ABox
repositories that appear to be complete w.r.t. a significant
portion of any DL-Lite TBox. The combination of these results
allows us to design OBDA systems in which redundancy is minimal,
the exponential aspect of query answering is notably reduced and
that can be implemented efficiently using existing RDBMSs.